Amazon.com was one of the first online retailers in the world. It started out with books and now sells nearly every consumer good, including groceries and over-the-counter medicines. The service is well known as one of the best places to find new or used books at prices below what you'd pay in most retail stores. It also features free shipping on many of its items.

One of the things that makes Amazon.com dynamic as an online retailer is its community of users, who write reviews and rate nearly every product on the service. Amazon.com is also transparent about which products are selling well in each category, which provides a secondary means for consumers to find out what's hot.

In addition to its retail commerce, Amazon also offers a service called S3, which provides large amounts of online storage at very low fees. While aimed at developers, S3 is used by many small and large businesses for its "pay-as-you-go" fee structure.